High Intensity Discharge (HID) lamps (e.g., high wattage metal halide lamp) convert input electrical energy into light energy by a relatively inefficient process. In particular, the conversion process uses the input electrical energy to increase the energy of electrons/ions in a plasma, and by their collision with neutral metal atoms in vapor phase, produces light. The energy of electrons/ions in a plasma, however, is a Maxwellian distribution, i.e., a small fraction of these energy particles are capable of exciting the metal atoms to the quantum states necessary to produce visible light. Per the process described above, the energy efficiency of converting the input electrical energy into useful light radiation is low, as only about 20% of input energy is converted to useful light radiation.
By contrast, due to the mechanism for light generation in Light Emitting Diodes (LED) lamps, the conversion efficiency is usually double, with about 40-50% of the input electrical energy being converted to useful light radiation. For LEDs, the mechanism of energy transfer from input to light generating mechanism is more efficient. In particular, light is generated when the conduction band electron re-combines with a hole in the valence band of the semi-conductor. The semiconductor is created by doping the dielectric with donor (n-type) or acceptor (p-type) atoms. An LED is created by a sandwich of these n-type and p-type materials, chosen such that the energy difference from conduction band to valence band is equal to the energy of the light emitted (i.e., desired frequency or wavelength). This sandwich is inherently a structure that has free electrons and holes, due to the fact that the temperature of the specimen is at a temperature which is greater than absolute zero. When an electric field is applied across the sandwich, energy is transferred to electrons and holes more directly by increasing the drift velocity of these particles. Thus, more electrons can make the transition from the valence band to the conduction band, creating holes, and these electrons thus recombine with holes generating the desired radiation.
While a standard high wattage Metal Halide lamp (e.g., an HID lamp), such as a 400 W lamp, typically has a system luminous efficacy of about 60 LPW, an equivalent LED lamp may often have a system efficacy of about 105 LPW. However, it is costly to replace HID lamps and the associated already installed pre-existing electrical components with LED fixtures.
Accordingly, the present inventors have recognized that a need exists for an improved LED lamp that may be operated on already installed HID electrical components and existing fixtures.